docs: def clusters(self):
          """returns the cluster object for each server"""
          if self._clusters is not None:
              self.__init()
              Cs = []
              for c in self._clusters:
                  url = self._url + "/%s" % c['clusterName']
                  Cs.append(Cluster(url=url,
                                    securityHandler=self._securityHandler,
                                    proxy_url=self._proxy_url,
                                    proxy_port=self._proxy_port,
                                    initialize=True))
              self._clusters = Cs
          return self._clusters